The present invention relates generally to batteries and battery packs and, more particularly, to a method of identifying the presence of an internal short within a cell of a battery or battery pack.
Internal-cell shorts may reduce the performance capability of, or cause hazardous conditions for, a battery pack. These shorts may be caused by manufacturing/design defects (e.g. metal-particle contamination that punctures the separator creating a path for electrons between the two electrodes or extends around an edge of the separator), poor cell design (e.g., a configuration permitting edges of the electrodes to touch, or metal contamination in the active material that dissolves and plates to form a bridge between the electrodes), or electrochemical abuse. Shorts caused by manufacturing defects have resulted in the recall of many lithium-ion batteries and have motivated significant improvements in manufacturing-quality control (e.g., implementation of clean manufacturing conditions, magnets to capture metal contamination, and the like). Through these improvements, the failure rate of lithium-ion batteries to thermal events caused by internal shorts in consumer applications has decreased to ˜1-5 ppm for the large-volume manufacturers. Internal-cell shorts may also be caused by battery aging (e.g. active material dissolution and plating). Because of the small, though finite possibility that an internal-cell short may form in one or more cells during the life of a battery pack, which may lead to performance degradation or hazardous operating conditions (e.g., excessive heat generation, over-discharge, and the like), it is important to identify the presence of cell shorts, particularly a presence of cell shorts during charging.
Typical battery cell packs used in electric vehicles (EVs) employ a multitude (e.g., thousands) of individual battery cells organized in sub-units (sometimes referred to as modules or bricks) that are interconnected. The cells and modules are combined variously in series and parallel to provide sustained high-energy storage and output as desired for any particular application.
Obtaining and evaluating specific and accurate information regarding an individual cell in this environment can be difficult. Data is evaluated individually and at a specific level but also takes into account macroscopic and gross level conditions of the application and battery pack to provide some context for the specific detailed information.
Accordingly, what is needed is an apparatus and method for identifying the presence of a short circuit in a battery pack.